Find your head register by yelling single syllable words such as "go," "hey" and "no." Notice how the sound of the words come from the upper part of your lungs as opposed to deep down in your chest. This is your falsetto.
Say the same words from your lower chest cavity and notice a change in the pitch. Even though you're saying the same words, you'll sound different than when you were saying them using your head register.
Stand with your feet hip distance apart and place your hands on your rib cage with the tips of your middle fingers touching. Take a deep breath and notice how your fingers separate, indicating your chest cavity has expanded.
Sing "Ho-la-la-ee-ay" alternating between your lower and upper range. The "Ho-la-la" should be in your lower range, the "ee" should be in your upper range and then return to your lower range for the "ay." Repeat yodeling the phrase.
Practice several times a day either outside, in the shower or someplace where you won't feel embarrassed. Through time, you'll notice improvement, and you'll gain confidence in your yodeling capabilities.